Messick, who was battling from depression for year and was recently diagnosed with bipolar disorder, committed suicide in Los Angeles, her family said in a statement, according to The Hollywood Reporter.
She served as McGowan's manager in 1997, the same year when Mcgowan's alleged rape by disgraced Hollywood producer Harvey Weinstein happened.
In the aftermath of multiple exposes that revealed the length and breadth of Weinstein's sexual transgressions, McGowan went public with her own account.
McGowan had claimed that Messick arranged the Weinstein meeting, which began in a hotel room.
Messick's name was further dragged into the headlines as part of an email exchange released by Weinstein, where his attorney Ben Brafman showed an email from Messick to show her alleged defence of his client.
Messick's family said the whole saga had a devastating effect on her as she was already battling depression.
They said that Messick became "collateral damage" in Hollywood's current campaign against sexual abuse.
"Jill was victimised by our new culture of unlimited information sharing and a willingness to accept statement as fact. She became collateral damage in an already horrific story," Messick's family said in the statement.
Her family accused McGowan of making "slanderous statements" against Messick.
"Over the past few months, many women have come out with allegations against Harvey Weinstein, including Rose McGowan, who has repeatedly spoken with the press, striking out against not only her alleged attacker, but a great many others.
"One of them was Jill, who chose to remain silent in the face of Rose's slanderous statements against her for fear of undermining the many individuals who came forward in truth," the statement said.
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